nounEtymology: Dutch, German, or Swedish, from Icelandic æthur, from Old Norse æthrDate: 17431. any of several large northern sea ducks (genera Somateria and Polystica) having fine soft down that is used by the female for lining the nest — called also eider duck2.eiderdown 1

eider — [ī′dər] n. pl. eiders or eider [ult. &LT; ON æthar, gen of æthr, eider duck] 1. any of several large sea ducks (esp. genus Somateria) that live in northern regions of Europe, Asia, and North America: often eider duck 2. EIDERDOWN (sense 1) … English World dictionary